Heat spells are incantations used to magically heat objects. They are elemental spells related to fire spells.
The known heat spells have been used in these occasions:
- Ahatian, used by Merlin to heat the sword of a bandit, forcing him to drop it and then killing him (The Moment of Truth).
- Forbaernan, by Merlin, unnoticed, to heat the knife that Aredian was holding at Morgana's throat. Merlin had used this incantation in several occasions as a fire spell (The Witchfinder).
- Onhǽte þá wæter, to make Arthur's bath water warmer. However, the spell was too powerful and the water became boiling hot (The Lady of the Lake).
- Non-verbally, by Gilli to win the semifinal match in the tournament, making his opponent drop his weapon (The Sorcerer's Shadow).
- Non-verbally, by Merlin. He cast a form of heat spell on Excalibur so that he could embed it in a stone in the middle of a forest (The Coming of Arthur: Part Two). The young warlock also seemed to have heated the stone when he freed the sword for Arthur (The Sword in the Stone: Part Two).
- The enchantment Merlin put on his pentacle for necromancy made it glow as if it was heated (Lancelot du Lac). This, however, might not have been a true heat spell, but an empowering, strengthening, or activating spell instead.
- The spell cast to copy a page used by Morgana had the effect of heating the page the Witch "printed" on a piece of cloth (The Hunter's Heart).
- Morgana, disguised as "Hilda" with an ageing spell, cast a heat spell on Mithian's bracelet, who had tried to escape the witch and inform Arthur that his half-sister was in Camelot, keeping her under her power. Morgana did this to torture Mithian and punish her for her attempted treason. She threaten the Princess that if she hadn't cooperated, she would have buried her father, King Rodor, alive. When Mithian bent to the sorceress' wishes, Morgana broke the enchantment with a flash of her eyes (Another's Sorrow).